33(* Oil the Quantity of Curlonk Add Gas [Nor. 



emitted under ordinary circumstances by the person on whom he 

 operated. 



5. Nitric Acid. — The experiments with this acid were made in 

 June. Dr. F. commenced by taking f 5 ss. of it diluted with 

 water, and afterwards gradually increased the dose ; on the third 

 day of the experiment the quantity of carbonic acid was seven per 

 cent. ; on the sixth day, between six and seven per cent., as above 

 stated. On repeating also the experiment in August, nearly the 

 same results were obtained. 



Such is a short account of Dr. Fyfe's and my own experiments. 

 Perhaps it will not be amiss to close the subject with a few general 

 observations. 



With respect to the numbers here brought forward, as well as 

 those in my former paper, I wish it to be distinctly understood that 

 they do not represent the measures of the quantity of carbonic acid 

 emitted in any given time from the lungs, but the measures of the 

 power or capability of the lungs at any given time, to form or 

 throw oft' carbonic acid. This was not so distinctly pointed out in 

 my former communication as it ought to have been. What I mean 

 then to say is this, that the power or capability of the lungs for 

 forming and throwing off carbonic acid is greater at noon, &c. ; 

 and not that a greater quantity of it is actually thrown off at that 

 time than at any other. A greater quantity will indeed be thrown 

 off, cieteris paribus, on an equal number of similar respirations 

 being made in the same given time. But whether this be really the 

 case or not, I cannot pretend to determine. 



If the hypothesis which was formerly advanced be founded in 

 truth, it is evident that we have in these numbers a sort of relative 

 measure of the degree of energy of the nervous system; but 

 whether it be a measure of the energy of this system as it operates 

 through the medium of the blood, or the muscular apparatus of 

 circulation or respiration, or partly on all the three, I am unable to 

 decide ; that is to say, I do not precisely know whether the changes 

 under consideration are to be ascribed to differences in the state of 

 the blood itself, or to differences in the state of circulation or respi- 

 ration. Perhaps all these causes may contribute in some degree to 

 produce them. 



It is true that Dr. Fyfe did not observe at all these diurnal varia- 

 tions. But this has little or no weight, when the apparatus he 

 employed be considered ; since it was incapable of showing it, or 

 at least the variations would be so extremely small that they would 

 most likely escape observation. For my own part, I do not con- 

 sider either my own experiments, or his, entirely conclusive on any 

 one point. This is a thing that can hardly be settled by one or two 

 observers. Indeed nothing but the striking uniformity that has 

 occurred to me, and the little probability at present ot my being 

 able to repeat them in a less exceptionable manner, added to my 

 wish of correcting as above what I formerly advanced, would have 



